Project Summary/Abstract The connective tissue system of the lung is critical for normal physiology of ventilation, and is perturbed in a wide range of disease: degradation in chronic obstructive pulmonary disease, thickening in pulmonary fibrosis, and malformation in bronchopulmonary dysplasia. The major conducting airways and the alveoli develop from axial and peripheral connective tissues, respectively. The alveolar duct is thought to be the anatomic unit at which these two major connective tissue systems integrate, structured by cable line elements (CLE) containing elastin, that maintain alveolar surface area over a range of conditions. Despite its importance, how the CLE initially forms during development remains unclear. Our lab is in a unique position to study CLE formation in the early postnatal rat lung, whose development closely resembles human postnatal lung development. Our main methods include electrophoresis staining of rat lung thick-sections containing intact alveolar ducts, tissue stretching using a customized platform, and structured- illumination epifluorescence microscopy for 3D reconstruction. In the early rat lung, we have recently discovered marked broad random deposition of precursor tropoelastin ?spheres? into the primary septa by postnatal day 4, and conversion into adult-like CLEs by day 21. Since the absence of stretch during lung development is known to interfere with elastin architecture formation, this led to our hypothesis that the CLE forms in the developing lung as a result of a directional stretch field applied to a random distribution of tropoelastin spheres. We have induced the formation of CLE-like structures using mechanical stretch on lung tissue ex vivo, recapitulating this step of normal development. The overall goals of this proposal are to (1) map the developmental process by which the CLE forms from tropoelastin in the developing lung, and (2) experimentally manipulate stretch fields on lung tissue to clarify how directionality of a stretch field influences CLE formation. A better understanding of lung microstructure development is expected to have a positive impact for conditions in which the connective tissue architecture is affected, including chronic obstructive pulmonary disease, pulmonary fibrosis, and bronchopulmonary dysplasia. In this two-year project, Dr. Valenzuela will work under the close mentorship of his sponsor, Dr. Steven Mentzer (thoracic/transplant surgeon), and in collaboration with Dr. Akira Tsuda (expert in lung microstructure and development), within the highly collaborative environment of Brigham and Women?s Hospital at Harvard Medical School. This project will help develop Dr. Valenzuela into an independent researcher and leader in academic medicine.